The present invention relates to an apparatus for assembly of a brake monitor on a brake actuator of the type used for heavy vehicles, including tractor and trailer combinations, buses and the like, having a brake actuator.
Heavy-duty trucks, buses and other large vehicles are typically equipped with a pneumatic brake actuating system. The brake actuating system typically applies air under pressure to a service chamber of a brake actuator to move a diaphragm in a first direction. A piston having a push rod typically moves with the diaphragm and the push rod is connected to a linkage which actuates the vehicle brakes. An emergency chamber having a power spring and a second diaphragm is typically mounted on the service chamber and is operable to move the push rod and actuate the brakes in the event that the pneumatic vehicle system fails or when the vehicle is turned off when the vehicle is parked. Thus, the emergency chamber serves as an emergency braking system for the vehicle and a parking brake.
A brake actuator has a predetermined amount of available movement of the push rod or stroke of the push rod. The amount of movement of the push rod required to fully actuate the braking system of the vehicle should be carefully monitored, such that it is within the stroke of the push rod of the brake actuator. Excessive movement of the push rod can be created by one of several factors. Typically, excessive movement of the push rod is due to brake lining wear. As the brakes wear, more movement of the push rod is required to actuate the brakes. Further, if the linkages and connections between the push rod and the linkages, et cetera, bend or become loose or excessively worn, additional push rod movement is required to actuate the brakes. A combination of these several factors may sometimes cause the amount of push rod movement required to actuate the brakes approach the available push rod movement or stroke available from the brake actuator. As will be understood, this is an undesirable situation.
The prior art has proposed various methods and apparatus to monitor the push rod movement during actuation of the brake and provide some indication to operator or service personnel as to when there is excessive push rod movement, which is referred to as xe2x80x9coverstroke.xe2x80x9d As will be understood by those skilled in this art, a determination of when there is excessive push rod movement or overstroke is dependent upon the designed or rated stroke of the brake actuator. For example, the push rod of a typical brake actuator may include a brightly colored ring, which may also be painted on the push rod, which indicates an overstroke condition when the ring extends out of the brake actuator during actuation of the brakes. The ring may, however, be difficult to see because of the location of the brake actuators beneath the truck or trailer and accumulated road debris. Automatic slack adjusters located between the push rod and the foundation brake are also conventionally used, wherein the slack adjuster incrementally adjusts to compensate for slack in the braking system and to decrease the required push rod movement.
The prior art has also proposed various electronic monitoring systems which generally monitor either the stroke of the push rod or the movement of the linkages between the push rod and the foundation brake including the slack adjuster. However, there are several obstacles to be overcome. First, powering and monitoring electronic indicators on each brake actuator of an 18-wheel vehicle is costly. Further, the hostile environment in which the brake actuators are mounted beneath the vehicle can damage the monitoring system, particularly where there are exposed pistons, sleeves, sensors, et cetera. Finally, where the stroke of the push rod is monitored by the brake monitoring system, it is essential that the push rod stroke monitoring system be accurately assembled on the brake actuator and be able to withstand the hostile environment of the brake actuator. Finally, it is desirable that the components of the brake monitoring system be accurately assembled on the brake actuator.
The vehicle brake monitoring system disclosed herein and in the above-referenced co-pending patent application solves many of these problems by providing a reliable and relatively inexpensive brake monitor which is incorporated into and becomes part of the vehicle brake actuator. By incorporating the brake monitoring system in the brake actuator, the components are protected, providing greater reliability and reduced cost. The brake monitoring system includes a push rod sleeve which incorporates a first sensor element and a second sensor element is fixed relative to the housing to provide accurate location of the push rod to sense an overstroke condition and may be utilized to sense other brake conditions including a worn brake, a dragging brake condition and a normally functioning braking system. In the preferred embodiment, the first sensor element incorporated in the push rod sleeve is an elongated magnet, most preferably a magnet having north and south poles, and a xe2x80x9cnullxe2x80x9d point spaced between the north and south poles, and the second sensor element is a Hall-effect sensor which is most preferably located in a sensor sleeve which surrounds the push rod sleeve. The sensor sleeve may be located within the brake actuator housing and most preferably also serves as a stone shield preventing entry of foreign material into the brake actuator housing.
As will be understood by those skilled in this art, the accurate location of the magnet in the push rod sleeve on the push rod is critical to accurate monitoring of the push rod stroke. Because of the normal tolerances of vehicle brake actuators, it is critical to adjust the push rod sleeve on the push rod relative to the second sensor element on each brake actuator for reliable performance of the brake monitoring system. Another problem associated with brake monitoring systems for brake actuators is that there are at least three standard strokes for brake actuators which must be taken in to account when assembling the brake monitoring system on the brake actuator. The apparatus for assembling a brake monitor on a brake actuator of this invention assures accurate location of the push rod sleeve and first sensor element on the push rod relative to the second sensor element and may be utilized to assemble a brake monitor on brake actuators having different push rod strokes. The apparatus of this invention thereby assures accurate and reliable operation of the brake monitoring system.
The apparatus for assembling a brake monitor on a brake actuator of this invention may be used with any conventional brake actuator, wherein the brake actuator includes a housing having an end wall, an opening through the end wall and a reciprocating piston within the housing having a push rod extending through the opening in the housing end wall for actuation of a vehicle brake, particularly pneumatic brake actuating systems for heavy duty trucks, buses, trailers and other large vehicles. As set forth above, a typical brake actuator for heavy duty vehicles includes an enclosed housing, a flexible diaphragm generally having a peripheral edge secured between the housing members, a piston having a piston plate biased against the flexible diaphragm by a return spring and the piston includes a push rod which reciprocates through an opening in the end wall of the brake actuator housing to actuate the vehicle braking system. The brake actuator housing is connected to the pneumatic braking system of the vehicle whereby, upon actuation of the vehicle pneumatic braking system, the diaphragm is driven against the piston plate, which reciprocates the push rod to actuate the vehicle foundation brake. As will be understood by those skilled in this art, the brake actuator may also include an emergency or power spring chamber which actuates the vehicle braking system when the vehicle pneumatic pressure falls below a predetermined pressure or when the vehicle is turned off, serving as a parking brake.
As set forth above, the preferred embodiment of the brake monitor includes an annular push rod sleeve which surrounds the push rod having a first sensor element and which has slideable adjustment on the push rod to accurately locate the first sensor element in the push rod sleeve relative to a second sensor element fixed relative to the housing. In the preferred embodiment, the first sensor element is an elongated magnet preferably having north and south poles and a null point between the north and south poles, wherein the magnet field is zero. In the most preferred embodiment of the brake monitoring system, the annular push rod sleeve is comprised of two semicircular components integrally hinged for ease of assembly and the second sensor element is incorporated in a sensor sleeve surrounding the push rod sleeve which most preferably also serves as a stone shield for the brake actuator.
The apparatus for assembling a brake monitor on a brake actuator of this invention accurately positions and fixes the first sensor element in the push rod sleeve on the push rod relative to the second sensor element of the brake monitoring system thereby assuring accurate monitoring of the installation brake actuator. The apparatus includes an adjustment clamp member which releasably supports the push rod sleeve on the push rod which is moveable by a servomotor relative to the housing and the push rod, a programmable logic controller (PLC) which is operably connected to the second sensor element fixed relative to the brake actuator housing and includes a power supply having a predetermined voltage. The PLC then controls a servomotor to adjust the axial position of the sleeve on the push rod, thereby aligning the first and second sensor elements to a predetermined voltage. That is, the PLC controls the servomotor to accurately align the first and second sensor elements of the brake monitoring system to assure accurate monitoring of the stroke of the brake actuator.
As set forth above, in the preferred embodiment of the brake monitoring system, the first sensor element is an elongated magnet extending longitudinally in the push rod sleeve and the second sensor element is a Hall-effect sensor, wherein the PLC of the apparatus includes an analog card, and wherein the Hall-effect sensor continuously xe2x80x9creadsxe2x80x9d the voltage of the magnet as the push rod sleeve is adjusted axially on the push rod by the servomotor connected to the PLC. The installation apparatus then fixes the sleeve on the push rod when the predetermined voltage is sensed by the Hall-effect sensor. In the most preferred embodiment, the installation apparatus fixes the sleeve on the push rod by attaching a lock nut on the sleeve and the push rod, permanently attaching the sleeve on the push rod. As set forth above, in the most preferred embodiment, the magnet includes north and south poles and a null point spaced from one of the poles and the apparatus adjusts the sleeve axially on the push rod until the Hall-effect sensor reads the null point.
The installation apparatus further includes a reciprocal sleeve clamp configured to receive the sleeve and the sleeve clamp extends to the push rod and places the sleeve around the push rod. In the preferred apparatus, the housing chamber is first pressurized by the installation apparatus to extend the push rod through the end wall opening and the sleeve clamp is then extended to receive the push rod sleeve on the push rod. In the most preferred embodiment, where the sleeve comprises two generally semicircular sleeve components hinged along one edge portion, the sleeve clamp is configured to receive the push rod sleeve in an open configuration and the installation apparatus then reciprocates to place the push rod sleeve in the open configuration around the push rod and then closes and clamps the sleeve around the push rod, wherein the sleeve is then slideably positioned on the push rod for calibration as described above. In the most preferred embodiment, the push rod sleeve includes a radial key and the sensor sleeve includes a keyway which slideably receives the radial key of the sleeve, such that the first sensor element in the push rod sleeve is aligned with the second sensor element fixed relative to the housing during calibration.
In the preferred embodiment of the installation apparatus, the sensor sleeve is mounted within the housing in the opening through which the push rod extends prior to receipt of the push rod. The installation apparatus of this invention then inserts the push rod through the sensor sleeve and compresses the piston or push rod plate against the return spring and locks the push rod in the extended position prior to final assembly of the brake actuator and receipt of the push rod sleeve and calibration as described above. The installation apparatus for assembling a brake monitor on a brake actuator of this invention therefore assures reliable assembly and calibration of the brake monitoring system, preventing error and assuring reliable monitoring of the brake actuator. Other advantages and meritorious features of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.